As is well known, processing chambers (for example, and without limitation, processing chambers used to deposit semiconductor films and processing chambers used to etch semiconductor films) need to be cleaned periodically to remove residue formed whenever wafers or substrates are processed therein (for example, such processing chambers may be cleaned after one or more wafers are processed). To clean the processing chambers, a cleaning process is run for a period of time (“clean time”) that is dictated typically by a requirement that substantially all residue built up in the processing chambers be removed. Such cleaning processes typically include plasma processes.
Detecting an endpoint for a plasma cleaning process may be performed by monitoring radiation output from a plasma formed within the processing chamber. The endpoint is identified by detecting the presence, or absence, of particular chemical compositions within the processing chamber, as evidenced by an analysis of the monitored radiation. However, such plasma cleaning processes have been found to be disadvantageous in certain environments due to physical bombardment of interior components of the processing chamber by constituents of the plasma, such physical bombardment causing deterioration of these interior components.
A high density plasma, chemical vapor deposition (“HDP CVD”) processing chamber (such as one manufactured by Applied Materials, Inc. of Santa Clara, Calif., “Applied”) can be used in a wide range of applications, for example, and without limitation, to deposit a fluorine-doped silicon glass (“FSG”) film, to deposit an undoped silicon glass (“USG”) film, to deposit a phosphorus-doped silicon glass (“PSG”) film, to deposit a film used for shallow trench isolation (“STI”), and so forth. A periodic cleaning process is carried out after one or more deposition processes used in these applications. To avoid the above-described physical bombardment of interior components of the processing chamber, a typical cleaning process for the Applied HDP CVD processing chamber is a “dark” cleaning process, i.e., a chemical process wherein a plasma is formed remotely, i.e., external to the processing chamber, and wherein the remotely generated plasma is admitted to the processing chamber to perform the cleaning process.
FIG. 1 shows a pictorial representation of an Applied HDP CVD chamber. As shown in FIG. 1, HDP CVD chamber 100 includes heating-cooling plate 110, coil assembly 120, interior chamber walls 130, wafer support 140, throttle & gate valve assembly 150, turbo pump 160, foreline 165, roughing valves 170 and 180, turbo valve 190, remote plasma applicator 200, remote plasma injection tube 210, and remote plasma injection manifold 220. During a typical deposition process, deposition precursor gasses enter chamber 100 through nozzles pictorially shown as 230, 240, and 250, and gaseous deposition residues are exhausted from chamber 100 through throttle & gate valve assembly 150 and turbo pump 160. During such a typical deposition process, roughing valve 170 and turbo valve 190 are closed, and roughing valve 180 is open under the control of a controller (not shown). Further, during the deposition process, residues are formed on interior chamber walls 130. During a typical cleaning process, a plasma is generated in remote plasma applicator 200, the plasma flows through remote plasma injection tube 210, and through remote plasma injection manifold 220 into chamber 100. During such a typical cleaning process, roughing valve 170 and turbo valve 190 are open, and roughing valve 180 is closed under the control of the controller. The constituents of the remotely generated plasma interact with the residues to produce gaseous byproducts that are exhausted from chamber 100 through foreline 165 by a roughing pump (not shown).
As is well known, an optimum clean time for each application is a complex function of a number of variables including, without limitation: thickness of residue on interior surfaces of the processing chamber; temperature of interior components of the processing chamber at the inception of, and during, the cleaning process; deposition/sputter ratios used during a deposition process; and chemical composition of the residue. In accordance with prior art techniques, the above-described dark cleaning process is terminated (clean endpoint) after a predetermined time, i.e., the clean endpoint is determined in accordance with a “by-time” algorithm. However, such by-time algorithms are unreliable because, among other reasons, chamber cool down causes temperature variation that produces deposition process variation. Some prior art solutions for determining a clean endpoint for a dark cleaning process entail utilizing “burn boxes” to strike a plasma in the gaseous deposition byproducts. However, such solutions are problematic because they typically require the use of high voltages, are unreliable, and produce electrical noise problems.
In light of the above, there is a need in the art for method and apparatus for determining a clean endpoint for a dark cleaning process.